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So I’ve got an iMac that won’t boot up. When turned on there’s a faint sound from inside but nothing like a normal boot up. If the power button is held down and the power cord is plugged in the fan turns on very loudly. I purchased the tool to open it up and have inspected the LED diagnostic lights. The only light that comes on is LED #1. This is true when turning it on with the screen plugged in and also with it removed. Any suggestions with what my next step should be?
Replace the power supply: iMac Intel 27" EMC 2639 Power Supply Replacement The LED’s are on the logic board to the right of the RAM slots and between the RAM slot and the HDD sata connector LED #1 Indicates that the trickle voltage from the power supply has been detected by the main logic board. This LED will remain ON whenever the iMac is connected to a working AC power source. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power source is disconnected or the power supply is faulty. LED #2 Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly. LED #3 Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement. LED #4 Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.
Hi Roger B., I have the exact same problem with my imac 27 emc 2429. Only the first LED comes on when I plug it into the wall. When I pressed the power button, the fans came on for 2sec and turned off. I ordered a used psu on ebay and the same problem remained. I’m about to order a logic board. Could you test your psu and see if you get the same voltage at each pin as I show in the attached picture? If you get the same voltages with your working psu, then I would need to buy a new logicboard. Thanks!
